This invention relates to the processing of semiconductor wafers in a vacuum chamber and, more broadly, relates to apparatus and methods for reducing particulate contamination of workpieces processed in vacuum equipment.
The fabrication of integrated circuits utilizes a number of processes which involve the application of high energy beams onto semiconductor wafers in vacuum. These processes include ion implantation, ion beam milling and reactive ion etching.
Conventional ion implantation systems and other semiconductor wafer fabrication equipment utilize processing chambers which are maintained at high vacuum during ion implantation or other energy delivery. When such vacuum chambers are vented following processing, significant aerodynamic forces develop in the incoming vent gas. These aerodynamic forces dislodge trace particulates present on surfaces within the chamber, such as on the platen and on interior surfaces of the vacuum chamber and of the vacuum lock. The aerodynamic forces thereby mobilize the particulates, which then come to rest on the wafer surface being processed. In particular, the initial inrush of gas during an uncontrolled vent operation can create shock waves which render the trace particulates airborne and can deposit them on the wafer surface. The presence of such particulates contaminates the wafer surface, and thereby can render the resultant semiconductor inoperative.
Particulate contamination of semiconductor wafers is a recognized problem in commercial semiconductor manufacture. It causes a significant fraction of wafer production to be discarded, and hence reduces production yield. The problem of particulate contamination becomes more severe as very large scale integration (VLSI) technology advances and circuit dimensions become ever smaller. As circuit linewidth decreases so that linewidth approaches particulate size, this form of contamination results in an increased failure rate and decreased yield. Currently, particulates as small as one half micron can necessitate rejection of a semiconductor wafer.
One approach directed at reducing particulate contamination involves the use of clean room environments having filtration and precipition facilities for removing particulates from the processing environment. A significant population of particulates in the 0.5 micron range, however, can exist even in clean room environments.
Other conventional techniques for minimizing contamination include stringent cleaning of the vacuum chamber and vacuum lock surfaces. Another technique involves designing material-handling systems so that all handling mechanisms are beneath the wafer, whereby fewer particulates fall upon the wafer. While these techniques tend to reduce total particulate count, they do not assure a processing chamber entirely free of trace particulates.
Certain prior semiconductor wafer fabrication systems utilize sharply restricted gas inflow or vent rates during the entire vent operation, in an effort to reduce turbulence in the vacuum chamber and the vacuum lock and thereby to reduce particulate contamination. Such systems, however, have low wafer throughput due to the resultant prolonged vent times, for example in some instances of approximately three minutes. Total implantation time, in contrast, is typically a fraction of a minute and in some instances is no greater than fifteen seconds per wafer. A three-minute vent time is estimated to slow down total process time by approximately 25%. Such increases in total process time are detrimental in commercial semiconductor processing, in which a major objective is the attainment of high throughput. Conventional semiconductor wafer processing systems, in summary, do not attain low particulate contamination levels in combination with high throughput.
Accordingly, there exists a need for vacuum processing methods and apparatus, for semiconductor wafers and other workpieces, which provide reduced particulate contamination while maintaining high processing speeds and wafer throughput.
It is thus an object of the invention to provide improved vacuum processing methods and apparatus.
It is another object of the invention to provide methods and apparatus for rapidly venting a vacuum chamber or vacuum lock while preventing or reducing particulate contamination of the workpiece being processed.
It is a further object of the invention to provide methods and apparatus for reducing turbulent venting flow in the vacuum lock of vacuum equipment while maintaining enhanced vent rates and processing speeds.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.